Chemical Property databases

In addition to ChemNetBase above:

ChemIDplus - Dictionary of over 370,000 chemicals (names, synonyms, and structures) from National Library of Medicine's Specialized Information Service. Use the Advanced Search feature for chemical structure, property, and toxicity searching

ChemSpider - Royal Society of Chemistry source for 26 million structures, synonyms, trade names, and formulas, with links to properties, spectra, etc. Links to both authoritative journal content (links to SMC subscribed content will only work on campus for this free resource) and non-authoritative (Wikipedia) content, so confirm results with other sources.